Retrievable bridge plug



Oct. 3, 1961 w. F. CAROTHERS RETRIEVABLE BRIDGE PLUG 2 Sheets-Sheet lINVENTOR William F. Corothers Filed Jan. 14, 1958 ATTORNEY Fig.|

Oct. 3, 1961 w. F. CAROTHERS 3,

RETRIEVABLE BRIDGE PLUG Filed Jan. 14. 1958 i 2 Sheets-Sheet 2 Fig.3

YINVENTOR William F Corothers ATTORNEY Fig.2

3,002,562 RETRIEVABLE BRIDGE PLUG William Frank Carothers, Odessa, Tex.,assignor to M & B Fishing Tool Co., Inc Odessa, Tex., an corporation ofTexas FiledJan. 14, 1958, Ser. No. 708,912 3 Claims. (Cl. 166-125) Thisinvention relates to a retrievable bridge plug, and it concerns moreparticularly a well pipe or casing plug which is capable of beingreleased and withdrawn from the well pipe after it has served itspurpose.

The invention relates generally to a well pipe or casing plug of thetype adapted to be lowered into a Well on a suspension means and set atany desired depth within the well pipe for sealing oif fluid pressuresabove and below the plug, as in sand fracturing operations at differentlevels.

The plug herein described'is of the retrievable' type, which after oncebeing set may be released and withdrawn from the well pipe, asdistinguished from plugs of the non-retrievable type which either areleft in place perma-" A retrievable plug is used primarily as atemporary plugging means to enable the operator to change surfacefittings or to carry on other operations which require the,

shutting off of pressures at'some lower point in the well pipe.material. Moreover, they are used mostly in well producing operationsafter all drilling equipment has been dismantled or removed from thewell.

It is important that the retrievable type of plug be readi lyand surelyreleasable from the well pipe'after it has served its purpose. Failureto retrieve the plug may result in loss of time and money due to theexpense of setting up and operating heavy drilling or well pullingequipment and the loss of production which results from tying up thewell.

An object of the invention is to provide a retrievable plug which iseflicient in use and which can be readily and surely released andwithdrawn from the well pipe.

Another object of the invention is to provide a plug The invention willbe readily understood by referring to the following description and theaccompanying drawing, in which:

FIGS. 1 and 1A together comprise a sectional elevational view of aretrievable bridge plug embodying the invention, and a setting tooltherefor, showing the plug in its normal position while lowering it in awell casing, before expanding the slips whereby the plug is secured infixed position relative to the casing;

FIG. 2 is a fragmentary sectional elevational view, similar to the viewshown in FIGS. 1 and 1A, showing the setting tool in its releasedposition whereby the plug is disengaged therefrom; and

FIG. 3 is a fragmentary sectional elevational view of the plug, and aretrieving tool therefor, showing the plug connected to the retrievingtool whereby it may be withdrawn from the well or reset at a differentelevation, as desired.

Such plugs are seldom made of readily drillable Referring to FIGS. 1 and1A of the drawing, the numeral 1 designates a well casing. A retrievablebridge The plug 2 includes a tubular mandrel 4, which is externallythreaded at 5, adjacent its upper end,,for engagement by the internallythreaded lower end of a tubular member 6. The outside diameter of themandrel end for engagement by corresponding surfaces of the slip" jaws10, whereby the lower ends of the slip jaws 10 are anchored to theannular member 9 and are movable radially relative thereto.

A frusto-conical tubular expanding member 13, the

tapered peripheral surface of which is capable of engag-- ingcorresponding surfaces of the slip jaws it) to expand: them, uponmovement of the expanding member 13 longi.

tudinally relative to the slip jaws 10, surrounds the mandrel 4 and issupported upon the uppermost external-- shoulder 7.

A pair of elastic rings 14 surround the slip jaws 10;.- and are receivedin arcuate grooves provided therefor in the outer surfaces of the slipjaws 1%, whereby the slip: jaws 10 are yieldably restrained againstradial displace ment thereof.

The upper end of the expanding member 13 is cupshaped, and the innerwall thereof is inclined downwardly and radially inwardly. A cup shapedannular packer member 15, which is formed of resilient material, and theadjacent surfaces of which conform to the shape of theexpanding member13, is received in the upper end of,

the expanding member 13. The packer member 15 surrounds the mandrel 4,and extends upwardly and radially outwardly from the expanding member 13for engagement with the inner wall of the casing l.

The outside diameter of the tubular member 5 is I greater than theoutside diameter of the mandrel 4 adjacent its upper end, and the lowerend of the tubular member 6 forms a downwardly facing external shoulderfor engagement with the inside of the packer member 15;-

whereby the packer member 15 and the expanding member 13 are secured tothe mandrel 4.

The upper end of the tubular member 6 is externally, flanged, as at 16,and has an annular valve seat formed therein, as at 17. A cylindricalvalve housing 18 surrounds and slidably engages the tubular member 5.The, lower end of the valve housing 18 is internally flanged,-. as at19, for engagement with the under side of the flange 1 16 of the tubularmember 6.

The upper end of the valve housing 13 is internally threaded, as at 20,for engagement with the lower end of an elongated stem 21, which iscircular in transverse sec-' tion and has a central bore 22 formedtherein.

An annular valve plug 23, which is of smaller diam eter than theelongated stem 21 and comprises a downreceived in a peripheral grooveprovided therefor in the valve 23 for engagement with the inner wall ofthe tubular member 6.

One or more side ports 25 are formed in the valve.-

The arrangement is such that fluid may flow through the side ports 25,the

housing 18 intermediate its ends.

valve housing 18, the tubular member 6 and the mandrel 4 when the valvehousing 18 is in its uppermost position relative to the tubular member6. The elongated stem 21. and the valve housing 18 are capable ofsupporting the tubular member 6 and the mandrel 4.

A plurality of circumferentially spaced openings 26"? are formed in thevalve housing 18 adjacent its lower end. The openings 26 communicatewith the under side 3 of the flange 16 of the tubular member 6, wherebythe pressure above and below the flange 16 is equalized.

A circular member 27, which is of slightly smaller diameter than theelongated stem 21 and is positioned above it, has a central bore 28formed therein, beginning at its under side, for engagement by the upperend of an elongated rod 29, to which it is connected by a screw 30. Therod 29 is reciprocable in the bore 22 of the elongated stem 21, whichacts as a guide therefor, and extends downwardly through the tubularmember 6 and below the mandrel 4. A pair of resilient rings 31 arereceived in peripheral grooves provided therefor in the rod 29 forengagement with the bore 22 of the elongated stem 21.

The lower end of the rod 29 is threaded, as at 32, for engagement by ashoe 33, which is circular in transverse section and has a threadedcentral bore formed therein, beginning at its upper side. The shoe 33 isadditionally secured to the rod 29- by a set screw, shown in dottedlines.

A. plurality of elongated metal strips 34, which advantageously may bemade of spring steel and are arched intermediate their ends, are spacedcircumferentially about the shoe 33. Each of the strips 34 is connectedat its lower end to the peripheral surface of the shoe 33, as by a screw35, and is connected at its upper end to the peripheral surface of theannular member 9, below the slip jaws 10, as by a screw 36. Theintermediate portions of the strips 34 yieldably and frictionally engagethe inner wall of the casing 1, and act as guides for use in centeringthe tool. The strips 34 also resist downward movement of the annularmember 9, Which carries the slip jaws 10, and coact with the expandingmember 13 to expand the slip jaws 10.

The mandrel 4 is internally enlarged adjacent its lower end, as at 37,below the external shoulder 8. A spider '38, which surrounds the rod 29and serves as a guide therefor, is externally threaded, as at 39, forengagement with the internally threaded lower end of the mandrel 4. Aplurality of circumferentially spaced side ports 40 are formed in theinternally enlarged portion 37 of the mandrel 4, above the threadsconnecting it to the spider 38.

The setting tool 3 includes an inner cylinder 41 and an outer cylinder42, each of which is open at its lower end, the inner cylinder 41 beingreciprocable in the outer cylinder 42. The circular member 27 and theupper end of the elongated stem 21 are receivable in the inner cylinder41. Peripheral grooves 43 and 44 are formed in the circular member 27and the upper end of the elongated stem 21, respectively. Two sets eachcomprising a plurality of balls, numbered 45 and 46, are received incircumferentially spaced openings 47 and 48 formed in the inner cylinder41 for engagement, respectively, with the grooves 43 and 44, as shown inFIG. 1, whereby the plug 2 is secured to the setting tool 3.

Annular grooves 49 and 50 are formed in the inner wall of the outercylinder 42 for engagement with the balls 45 and 46, upon moving theinner cylinder 41 upwardly relative to the outer cylinder 42, wherebythe balls 45 and 46 are disengaged from the grooves 43 and 44, as shownin FIG. 2, and the plug 2 is released from the setting tool 3 and may bewithdrawn therefrom. The spacing of the grooves 49 and 50 is such thatthe elongated stem 21 is released before the circular member 27 isreleased, whereby the expanding member 13 is advanced downwardlyrelative to the slip jaws 10, to expand the slip jaws 10.

The upper end of the outer cylinder 42 is internally threaded, as at 51,for engagement with an externally threaded collar 52, which is alsointernally threaded, as at 53, for engagement with the lower end of acylindrical member 54.

An elongated rod 55 is threaded at its lower end,

4. as at 56, for engagement with a threaded bore formed in the upper endof the inner cylinder 41. The rod 55 supports the inner cylinder 41 andthe plug 2, as shown in FIGS. 1 and 1A, and is reciprocable in a centralbore 57 formed in the cylindrical member 54 beginning at its lower end.4

The cylindrical member 54 is internally enlarged to form. a pair oflongitudinally spaced, upwardly facing internal shoulders 58 and 59. Acompression spring 60 is received inthe cylindrical member 54, above thelowermost internal shoulder 59, and surrounds the rod 55. A cylindricalenlargement 61, which is formed on the rod 55 intermediate its ends, ispositioned in the cylindrical member 54 above the uppermost internalshoulder 58, and is acted on by the spring 69 whereby it is urgedupwardly therein. The shoulder 58 limits the downward movement of therod 55 relative to the cylindrical member 54.

The upper end of the cylindrical member is exteinally threaded, as at62, for engagement with the internally threaded lower end of a swagedmember 63, the outside diameter of which is reduced intermediate itsends to form an upwardly facing external shoulder 64. The upper end ofthe rod 55 is reciprocable in a central bore 65 formed in the upper endof the swaged member 63.

The up er end of the swaged member 63 is externally threaded, as at 66,for engagement with the internally threaded lower end of a connectingmember 67. The connecting member 67 has a counter bore 63 which isaligned with the bore 65 of the swaged member 63, and in. which theupper end of the rod 55 is reciprocable. The upper end of the connectingmember 67 is externally threaded, as at 69, for engagement with asuspension means 70, which advantageously may be a. wire line or cable.

A peripheral groove 71 is formed in the upper end of the rod 55 forengagement by a plurality of balls 72, which are received incircumferentially spaced openings provided therefor in the upper end ofthe swaged member 63, above the external shoulder 64. A collar 73, whichsurrounds the upper end of the swaged member 63. normally acts upon theballs 72 to retain them in engagement with the groove 71, whereby therod 55 is restrained against longitudinal movement relative to theswaged member 63.

The collar 73 has an annular groove 74 formed in its inner wall,adjacent its upper side. As shown in FIG. 2, upon movement of the collar73 downwardly relative to the swaged member 63, the balls 72 arereceivable in the annular groove 74 of the collar 73, whereby the rod 55is disengaged from the swaged member 63 and is urged upwardly relativethereto, by the action of the spring 60. to release the plug 2 from thesetting tool 3 as above dcscribed. This is accomplished by dropping a godevil shown in dotted lines, from the surface for engagement with thecollar 73.

A compression spring 75, which surrounds the upper end of the swagedmember 63 and is received in an annular groove 76 formed in the underside of the collar 73, acts upon the external shoulder 64 and the underside of the collar 73 whereby the collar 73 is normally urged upwardlyin engagement with a downwardly facing external shoulder formed by thelower end of the connecting member 67.

Referring to FIG. 3 of the drawing, a retrieving tool for use inwithdrawing the plug 2 from the well casing 1, and for resetting it atdifferent elevations, is indicated generally by the numeral 77.

The retrieving tool 77 includes an inner cylinder 78 and an outercylinder 79, each of which is open at its lower end, the inner cylinder78 being reciprocable in the outer cylinder 79. The circular member 27and the upper end of the elongated stem 21 are receivable in the innercylinder 78. A plurality of balls 89 are received in circumferentiallyspaced openings 81 formed in the inner cylinder 78 for engagement with aperipheral groove 44 formed in the upper end of the elongated stem 21,whereby the plug 2 is secured to the retrieving tool 77.

The outer cylinder 79 is internally enlarged at 82, above its lower end,to form an upwardly facing internal shoulder 83. The inner wall of theouter cylinder 79 normally engages the balls 80 to retain them inengagement with the peripheral'groove 44 formed in the upper end of theelongated stem 21. The arrangement is such that the balls 80 aredisengaged from the groove 44, upon moving the inner cylinder 78upwardly relative to the outer cylinder 79, whereby the plug 2 may besnapped on the retrieving tool 77, or alternatively, may be released andwithdrawn therefrom.

The upper end of the outer cylinder '79 is internally threaded, as at84, for engagement with the externally threaded lower end of acylindrical member 85.

The lower end of an elongated rod 86 is passed through a central bore 87formed in the upper end of the inner cylinder '78, and is threaded forengagement by a nut 88 positioned below the lower end of the bore 87.The rod 86 supports the inner cylinder 78 and the plug 2, as shown inFIG. 3, and is reciprocable in a central bore 89 formed in the lower endof the cylindrical member 85.

A compression spring 90, which is received in depress ions 91 and 92formed in the upper end of the inner cylinder 78 and the lower end ofthe cylindrical member 85, yieldably restrains the inner cylinder 78against up-- ward movement relative to the outer cylinder 79, where:

by the plug 2 may be snapped on the retrieving tool 77. The cylindricalmember 85 is internally enlarged to form a pair of longitudinallyspaced, upwardly facing internal shoulders 93 and 94. A compressionspring 95, which is substantially stronger than the spring 90, isreceived in the cylindrical member 85, above the lowermost internalshoulder 94, and surrounds the rod 86. A cylindrical enlargement 96,which is formed on the rod 86 intermediate its ends, is positioned inthe cylindrical member 85 above the uppermost internal shoulder 93, andis acted upon by the spring 95 whereby it is urged upwardly therein. Theshoulder 93 limits the downward movement of the rod 86 relative to'thecylindrical member 85.

The upper end of the cylindrical member 85 is externally threaded, as at97, for engagement with the internally threaded lower end of a swagedmember 98, the outside diameter of which is reduced intermediate itsends to form an upwardly facing external shoulder 99. The upper end ofthe rod 86 is reciprocable in a central bore 100 formed in the upper endof the swaged member 98.

The upper end of the swaged member 98 is externally threaded, as 'at101, for engagement with the internally threaded lower end of aconnecting member 102. The connecting member 102 has a counter bore 103which is aligned with the bore 100 of the swaged member 98,- and inwhich the upper end of the rod 86 is reciprocable. The upper end of theconnecting member 102 is connected to a suspension means (not shown),which advantageously may be a wire line or cable.

A peripheral groove 104 is formed in the upper end of the-rod 86 forengagement by a plurality of balls 105, which are received incircumferentially spaced openings provided therefor in the upper end ofthe swaged member 98, above the external shoulder 99. A collar 106,which surrounds the upper end of the swaged member 98, normally actsupon the balls 105 to retain them in engagement with the groove 104,whereby the rod 86 is restrained against longitudinal movement relativeto the swaged member 98.

The collar 106 has 'an annular groove107 formed in its inner wall,adjacent its upper side. Upon movement of the collar 106 downwardlyrelative to the swaged member 98, the balls 105 are receivable in theannular groove107 of the collar 106, whereby the rod 86 is dis,-

engaged from the swaged member 98 and is urged'upwardly relativethereto, by the action of the spring 95, to release the plug 2 from theretrieving tool 77 as above described. This is accomplished by droppinga go devil (not shown) from the surface for engagement with the collar106,

A compression spring 108, which surrounds the upper end of the swagedmember 98 and is received in an annular, groove 109 formed in the underside of the collar 106, acts upon the external shoulder 99 and the underside of the collar 106 whereby the collar 106 is normally urged upwardlyin engagement with a downwardly facing external shoulder formed by thelower end of the connecting member 102.

The operation of the apparatus above described is as follows:

The relative positions of the parts, upon lowering the bridge plug 2inthe casing 1 on the setting too-1 3, is as shown in FIGS. 1 and 1A.The valve 23 is open, and well fluids pass upwardly through the ports 25as the apparatus is lowered in the well bore.

The function of the slip jaws 10 is to support the bridge plug2 at thedesired elevation in the casing 1. The weight of the elongated member21, and the parts depending therefrom, as shown in FIGS. 1 and 1A, isrelied onto prevent upwarddisplacement of the expanding member 13relative to the; slip jaws 10, due to fluid pressure from below, afterthe slip jaws 10 have been set. The weight of the elongated member 21also prevents opening of the valve 23.

Upward displacement of the expanding member 13 and the packer member, 15in response to fluid pressure from below, to thereby disengage the slipjaws 10 from the casing 1, is prevented by expansion of the packer member 15, due to the static head of well fluids above it, whereby thepacker member 15 frictionally engages the casing 1, and preventswithdrawal of the bridge plug 2 therefrom, until the valve 23 is opened.

The static head, of well fluids in the casing 1 not only acts onthepacker member 15 to expand it, and to resist upward displacement thereofin response to fluid pressure from below, but also acts on the elongatedmember 21 and the circular member 27 alike to prevent upwarddisplacement of the bridge plug 2.

The static head of well fluids in the casing 1i, acting on the elongatedmember 21, resists opening of the valve 23.

Upward displacement of the expanding member 13 and the packer member 15in response to fluid pressure from below is also prevented by reason ofthe fact that the same upward pressure which acts on the expandingmember 13 and the packer member 15 also acts on the under side of theshoe 33, to which the slip jaws 10 are connected, as above described.

The cross sectional area of the valve 23 is comparatively small,relative to the cross sectional area of theelongated member 21, so thatthe weight of the elongated member 21, together with the static head ofwell fluids acting thereon, ordinarily is sufiicient to prevent thevalve 23 from being unseated by upward fluid pressure in the well.

The packer member 15 is not collapsed due to fluid pressure from belowfor the reason that it is of substantially the same diameter as theexpanding member 13 be low it, and for the further reason that thepacker member 15 is expanded, whereby it frictionally engages the casing1, by the static head of well fiuids above it.

FIG. 3 shows the relative positions of the parts upon attaching thebridge plug 2 to the retrieving tool 77. The relative positions of theparts upon withdrawing the bridge plug 2 from the casing 1 is the sameas shown in FIGS. 1 and 1A, above referred to. The valve 23 is openedand the slip jaws 10 are disengaged from the casing 1 upon upwardmovement of the bridge plug 2 and the retrieving. tool 77.

The invention may be modified in various ways without departing from thespirit and scope thereof.

The strips 34, which yieldably and frictionally engage the inner wall ofthe casing 1, resist downward movement of the annular member 9, whichcarries the slip jaws 10, and coast with the expanding member 13 toexpand the slip jaws, as above described.

The weight of the setting tool 3, acting on the rod 29 and the shoe 33,to which the strips 34 are attached, is sulficient to overcome thefrictional resistance of the strips as to downward movement of thebridgeplug 2., whereby the bridge plug 2 may be lowered in the casing 1.

FIG. 2 shows the relative movement of parts whereby the bridge plug 2 isdisengaged from the setting tool 3. The spacing of the grooves 49' and50 is such that the elongated member 21 is released before the circularmember 27 is released, whereby the expanding member 13 is advanceddownwardly relative to the slip jaws 10, to expand the slip jaws it asabove described.

The weight of the elongated member 21 is suflicient to overcome anyfrictional resistance of the rings 31 to relative movement between therod 29, to which the circular member 27 is attached, and the elongatedmem ber 21.

The valve 23 is closed upon downward movement or the elongated member 21and the valve housing 18 relative to the tubular member 6, uponeiipanding the slip jaws as above described.

What is claimed is:

l. A retrievable bridge plug, adapted to be set in a well pipe to sealoil: pressures from below, comprising a tubular mandrel, a tubularmember connected by threads to the upper end of the mandrel, the lowerend of the tubular member forming a downwardly facing external shoulderand the outside diameter of the mandrel being reduced intermediate itsends to form a pair of longitudinally spaced, upwardly facing externalshoulders, an annular member surrounding the mandrel and supported uponthe lowermost external shoulder, a plurality of circumferentially spacedslip jaws supported for radial movement upon the annular member, atubular expanding member surrounding the mandrel and supported upon theuppermost external shoulder, the expanding member having a taperedperipheral surface for engagement with corresponding surfaces of theslip jaws to expand them, upon movement of the expanding memberdownwardly relative to the slip jaws, a cup shaped annular packermember, formed of resilient material, surrounding the mandrel andclamped between the upper end of the expanding member and the lower endof the tubular member, the packer member extending upwardly and radiallyoutwardly from the mandrel for engagement with the well pipe, acylindrical valve housing surrounding the tubular member, the tubularmember being externally flanged at' its upper end and the lower end ofthe valve housing being internally flanged for sliding engagement withthe tubular member below its flanged upper end, an elongated member,circular in transverse section and having a central bore formed therein,connected by threads to the upper end of the valve housing, an annularvalve plug, of smaller diameter than the elongated member and comprisinga downward extension thereof, extending downwardly into the valvehousing for telescoping engagement with the upper end of the tubularmember, one or more side ports being formed in the valve housingintermediate its ends whereby fluid may flow through the valve housing,the tubular member and the mandrel when the valve housing is in itsuppermost position relative to the tubular member, a circular member, ofsmaller diameter than the elongated member, positioned above theelongated member, the circular member and the upper end or"- theelongated member each having a peripheral grooveformed therein forengagement by a setting tool, an elongated rod connected at its upperend to the circular member and reciprocable in the bore of the elongatedmember,

the rod extending dswnwardly through the tubular memher and below themandrel, a circular shoe connected to the lower end of the rod, and aplurality of circumferentially spaced resilient metal strips eachconnected at their ends to the annular member and the shoe, the metalstrips being bowed radially outwardly intermediate their ends foryicldable, frictional engagement with the well pipe.

2. In combination with a retrievable bridge plug as described in claim1, a setting tool comprising an inner cylinder and an outer cylinder,each open at its lower end, the inner cylinder being reciprocable in theouter cylinder, the circular member and the upper end of the elongatedmember being receivable in the inner cylinder, two sets each comprisinga plurality of balls received in circum' ferentially spaced openingsformed in the inner cylinder for engagement with the peripheral groovesformed in the circular member and the upper end of the elongated member,respectively, whereby the plug is secured to the setting tool, annulargrooves being formed in the inner wall of the outer cylinder forengagement with the two sets of balls upon moving the inner cylinderupwardly relative to the outer cylinder, whereby the balls aredisengaged from the peripheral grooves of the circular member and theupper end of the elongated member and the plug is released from thesetting tool, the spacing of the annular grooves being such that theelongated member is released efore the circular member is released,whereby the expanding member is advanced downwardly relative to the slipjaws, to expand them, a cylindrical member removably connected at itslower end to the upper end of the outer cylinder, an elongated rodconnected at its lower end to the upper end of the inner cylinder andreciprocable in a central bore formed in the cylindrical memberbeginning at its lower end, the cylindrical member being internallyenlarged to form a pair of longitudinally spaced, upwardly facinginternal shoulders, a compression spring reeived in the cylindricalmember, above the lowermost in ternal shoulder and surrounding the rod,a cylindrical en largement, formed on the rod intermediate its ends,positioned in the cylindrical member above the uppermost internalshoulder, and acted on by the spring whereby it is urged upwardlytherein, a swaged member removably connected at its lower end to theupper end of the cylindrical member, the outside diameter of the swagedmemher being reduced intermediate its ends to form an upwardly facingexternal shoulder, the upper end of the rod being reciprocable in acentral bore formed in the upper end of the swaged member, a connectingmember adapted to be suspended from the surface and removably connectedat its lower end to the upper end of the swaged member, the connectingmember having a bore aligned with the bore of the swaged member and inwhich the upper end of the rod is reciprocable, a peripheral groove beinformed in the upper end of the rod, a plurality of balls received incircumferentially spaced openings pro-- vided therefor in the upper endof the swaged member, a collar surrounding the upper end of the swagedmember and normally acting upon the balls to urge them in em gagementwith the peripheral groove of the rod, whereby the rod is restrainedagainst longitudinal movement relative to the swaged member, the collarhaving an annular groove formed in its inner wall, adjacent its upperside, the balls being receivable in the annular groove of the collar,upon movement of the collar downwardly relative to the swaged member,whereby the rod is disengaged from the swaged member and is urgedupwardly relative thereto, by the action of the compression spring, torelease the plug from the setting tool, and a compression springsurrounding the upper end of the swaged member and acting upon theexternal shoulder and the under side of the collar whereby the collar isyieldably retained in its uppermost position relative to the swagedmember.

3. In combination with a removable bridge plug having a stem comprisingan elongated member having a rod reciprocally arranged therethrough andslips in said plug adapted to be actuated by said rod, and a pluralityof circumferential grooves in the upper end of said stem and said rod, aretrieving tool for said bridge plug, comprising, an outer cylinder, andan inner cylinder reciprocal in said outer cylinder, and adapted toreceive said stem and said rod, a plurality of balls incircumferentially spaced openings in the lower end of said innercylinder and engageable with the grooves in said stern and said rodwhereby said plug is secured to said inner cylinder, annular grooves inthe inner wall of said outer cylinder adapted to receive said balls andrelease the same from the grooves in said stem and said rod when saidouter cylinder is moved longitudinally of said inner cylinder, acylindrical member connected to the upper end of said outer cylinder, asecond rod connected to the upper end of said inner cylinder andextending concentrically through said cylindrical member, annularshoulders formed in the upper and lower portions of said cylindricalmember, an

enlargement formed on said second rod intermediate its ends engageablewith said upper shoulder, a compression spring embracing said second rodin said cylindrical member below said enlargement and engaging the undersurface thereof and said lower shoulder, whereby the inner cylinder isbiased upwardly in said outer cylinder when the stem of said bridge plugis released therefrom, means for suspending said retrieving tool in awell, and releasable means for connecting said suspending means to theupper 10 end of said second rod.

References Cited in the file of this patent UNITED STATES PATENTS 152,217,986 Knox Oct. 15, 1940 2,401,119 Taylor May 28, 1946 2,644,527Baker July 7, 1953 2,776,015 Bielstein Jan. 1, 1957 2,799,346 Baker etal July 16, 1957

